US2261485A - Telephone system - Google Patents

Description

Nov. 4, 1941. s. E. PETERSON ETAL 2,261,485

TELEPHONE SYSTEM Filed April 11, 1940 e Smeets-sheet 1 Nov. 4, 1941. s..E. PETERSON ETAL 2,261,485

TELEPHONE SYSTEM -Filed April 11, 1940 e sheets-sheet 3 Nov. 4, '1941. s. E. PETERSON E-r AL I 2,251,485

TELEPHONE SYSTEM Filed April 11, 1940 6 sheets-sneek 4 Quik@ QA .I

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n TELEPHONE 'SYSTEM e shefs-sheet 5 Filed AprilV ll, 1940 SETH E. PETERSON MORRIS E. GRIFFINS Mil MMR ATTORNEYS Nov. 4, 1941.

s. E. PETERSON ErAl.

. TELEPHONE SYS TEM Filed April4 l1, 1940 6 Sheets-Shea?I -6 INVENTORS SETH E. PETERSON MORRIS E. GRIFFINS ATTORNEYS Patented Nov. 4, 1941 2,261,485 TELEPnoNEsYsTEM Seth E. Peterson, Chicago, and Morris E. Griflins, Riverside, Ill., assigncrs to Associated Electric Laboratories, Inc., Chicago, Ill., a corporationL of Delaware Application April 11, 1940, Serial No. 329,086

43 Claims. (Cl. 179-27) The present invention relates to telephone systems and more particularly to improvements in telephone systems of the semi-automatic type.

In a telephone system of the semi-automatic type a call initiated on a telephone line is automatically extended by associated switching apparatus to an operator position to be answered; and after the call is answered at the operator position, the operator thereat controls an associated switch train to eXtend the call to the desired destination. In a telephone system of this character the switch train associated with the operator position frequently comprises diierent types of automatic switches, rendering it necessary for the operator to manipulate corresponding different types of calling devices at the operator position in order to control the different types of automatic switches in the associated switch train. As a result of this type of control, a larger number of errors is made and more delay is encountered at the operator position in extending calls than is desirable.

Accordingly, it is an object of the present invention to provide in a telephone system of the type described comprising an operator position and a switch train including a number of different types of automatic switches, an improved unitary calling device at the operator position which is operative selectively to control indiscriminately the different types of automatic switches in the associated switch train,

Another object of the invention is to provide in a telephone system of the type described including an operator position, improved switching apparatus for routing calls to the operator position to be answered.

Another object of the invention is to provide in a signaling system, an improved register arrangement for selectivelycontrolling the operation of an associated automatic'switch.

Another object of the invention is to provide in a signaling system, an improved register arrangement for selectively controlling the operation of an associated `repeater which is operative to repeat switch control impulses.

A further object of the invention is to provide in a signaling system, an improved repeater which is operative to repeat switch control impulses.

A further object of the invention is to provide in a signaling system comprising a repeater which is operative to repeat switch control impulses; an improved arrangement including an impulse generator for selectively controlling the operation of the repeater.

A further object of the invention is to provide in a signaling system comprising a number of repeaters each of which is operative to Arepeat switch control impulses, an improved arrangement including an impulse generator commonly associated with the repeaters for selectivelycontrolling the operation of the repeaters A further object of the invention is to provide in a signaling system, an improved impulse generator which is adapted to be utilized in a repeater network.

The features of the present invention are illustrated as being incorporated `in ay telephone system comprising a central exchange-'terminating a plurality of manual telephone lines and a distant exchange terminating a plurality of manual telephone lines, the central exchange and the distant exchange being interconnected by` two groups of one-way trunk lines extending therebetween. The central exchange comprises an operator switchboard provided with a vnumber of operator positions; and each exchange comprises an automatic switch train', the automatic switch train in the central exchange including'a repeater network.

In accordance with one feature of the invention the telephone system comprises a trunk including rst and second line conductors, switching apparatus having access to the trunk, an automatic switch terminating the trunk, a plurality of lines accessible to the automatic vswitch,means for causing the automatic switching apparatus to seize the trunk when the trunk is idle, means controlled by the seizure of the trunk for impressing a predetermined potential upon the Yiirst line conductor of the trunk, means controlled when the predetermined potential is impressed upon the :drst line conductor of the trunk for conditioning the automatic switch, and means controlled when the automatic switch is conditioned for rendering busy the trunk. Also the system' comprises means for operating the automatic switch after it is conditioned, thereby to cause the automatic switch to seize one of the lines, and means for initiating the release of the automatic switch, the automatic switch being so connected and arranged that it is adapted to be completely released when the release thereof is initiated. Further the system comprises means controlled in the event theautomatic switch fails completely to release for impressing a predetermined potential upon the second line conductor of the trunk, and means controlled when the predetermined potential is impressed upon the second line conductor of the trunk for rendering busy the trunk Further the system comprises a given telephone line associated with the switching apparatus, the switching apparatus being operated in response to the presence of a calling condition upon the given telephone line to seize the trunk when the trunk is idle. Also the telephone system comprises an operator position, means controllable from the operator position for selectively operating the automatic switch, the automatic switch being operative in a rst predetermined manner to seize one of the lines accessible thereto and in a second predetermined manner without seizing one oi the lines accessible thereto, means included in the automatic switch and controlledby the operation thereof in the second manner for causing the release of the automatic switch, and means controlled by the release of the automatic switch for rendering idle the trunk and for locking out of service the given telephone line in the event there is a calling condition thereon.

In accordance with another feature of the invention the system comprises a register, means for registering diierent digits in the register, an automatic switch including a switching mechanism and an impulse responsive motor for operating the switching mechanism and an impulse transmitter operative to transmit impulses to the motor, means for connecting the register to the switch, means for initiating operation of the impulse transmitter, means controlled revertively from'the switch in accordance with the operation of the impulse transmitter to transmit impulses to the motor for clearing the register of the digit registered therein, whereby the register is cleared of the digit registered therein when the number of impulses transmitted from the impulse transmitter to the motor corresponds to the digit registered in the register, and means controlled when the register is cleared of the digit registered therein for arresting operation of the impulse transmitter. More particularly, the impulse transmitter in the switch is of the step-by-step type, the impulse transmitter being operative to transmit a direct impulse to the motor and a revertive impulse to the register upon each step thereof; and the control arrangement for the impulse transmitter includes means for initiating step-by-step operation of the impulse transmitter, and means controlled when the number of revertive impulses transmitted from the impulse transmitter to the register corresponds to the digit registered therein for arresting stepby-step operation of the impulse transmitter.

In accordance with a further feature of the invention the system comprises a repeater including an impulse transmitter operative to transmit impulses from the repeater, means for connecting the register to the repeater, means for initiating operation of the impulse transmitter, means controlled revertively from the repeater in accordance with the operation of the impulse transmitter for clearing the register of the digit registered therein, whereby the register is cleared of the digit registered therein when the number of impulses transmitted from the repeater corresponds to the digit registered in the register, and means controlled when the register is cleared of the digit registered therein for arresting operation of the impulse transmitter. More particularly, the transmitter in the repeater is operative to transmit switch control impulses and register control impulses at a predetermined rate and the arrangement for controlling the operation of the repeater includes means for initiating operation of the impulse transmitter and means merges -controlled when the number of register control impulses transmitted from the impulse transmitter to the register corresponds to the digit registered therein for arresting operation of the impulse transmitter.

In accordance with a further feature of the invention the system comprises a number of registers, means for registering diil'erent digits in the registers, switching means operative through a number of cycles successively to connect and disconnect the registers and the repeater, the switching means being operative through a given cycle to connect a given register to the repeater and then to disconnect the given register from the repeater, the impulse transmitter included in the repeater being operative through a cycle to transmit a series of switch control impulses, means for initiating a cycle of operation of the switching means, means controlled when a register is connected to the repeater for initiating a cycle of operation of the impulse transmitter, and means controlled revertively from the repeater in accordance with the operation" of the impulse transmitter for completing a cycle of operation of the switching means and then for initiating another cycle of operation of the switching means, whereupon one of the registers is disconnected from the repeater and then another of the registers is connected to the repeater, the last-mentioned means being controlled when the number of impulses transmitted from the repeater corresponds to the digit registered in the one of the registers. Further the system comprises means controlled when a cycle of operation of the switching means is completed for completing a cycle of operation of the impulse transmitter.

In accordance with a further feature of the invention the system comprises an impulse generator, means for connecting the register to the repeater and for connecting the repeater to the impulse generator, means controlled when the repeater is connected to the impulse generator for initiating operation of the impulse transmitter, means controlled when the number of impulses in the series of register control impulses transmitted from the impulse transmitter to the register corresponds to the digit registered therein for disconnecting the register from the repeater, and means controlled when the register is disconnected from the repeater for arresting operation of the impulse transmitter and for disconnecting the repeater from the impulse generator. More particularly, the impulse generator is operative repeatedly through a cycle to transmit a start impulse and then at least one control impulse; and the arrangement for controlling the repeater includes a control network operative to condition the impulse transmitter in response to a start impulse transmitted from the impulse generator and then to cause operation of the impulse transmitter after it is conditioned in response to control impulses transmitted from the impulse generator, thereby to prevent operation of the impulse transmitter to transmit a series of switch control impulses including a mutilated switch control impulse, and means for selectively operating the control network, thereby to cause the repeater to transmit a series of switch control impulses comprising different numbers of switch control impulses.

In accordance with a further feature of the invention the system comprises a repeater network including a number of individual repeaters commonly associated with the impulsing generator, a number of calling devices, means for selectively connecting the calling devices to the repeaters, and means including the calling devices for selectively controlling the operation of the repeaters from the impulse generator. More particularly, the repeater network is so connected and arranged that operation of the impulse generator is initiated when one of the repeaters is connected thereto, and operation of the impulse generator is arrested when each of the repeaters is disconnected therefrom.

In accordance with a further feature of the invention the impulse generator comprises a control network including rst and second relays, first and second conductors, and means for impressing cyclically at a predetermined rate upon the first conductor and then upon the second conductor a predetermined potential, the control network being so connected and arranged that each odd time the potential is impressed upon the first conductor the first relay is operated, each o'dd time the potential is impressed upon the second conductor the second relay is operated, each even time the potential is impressed upon the first conductor the rst relay is restored, and each even time the potential is impressed upon the second conductor the second relay is restored, whereby the rst and second relays are controlled cyclically at one-half the predetermined rate. Also the impulse generator includes an impulse transmitting network governed by the cyclical control of the first and second relays. Also the impulse generator includes a signal and means governed by a predetermined departure by the first and second relays from the cyclical control at one-half the predetermined rate for controlling the signal.

In accordance with a further feature of the invention the network in the impulse generator comprises a timing relay, iirst and second condensers, a first series circuit for charging the first condenser and for energizing the relay, a second series circuit for charging the second condenser and for energizing the relay, a first series path for discharging the rst condenser and for energizing the relay, a second series path for discharging the second condenser and for energizing the relay, cyclically operating control means for completing the first circuit'and the second path and then for completing the second circuit and the rst path, thereby intermittently to energize the timing relay in order to cause intermittent operation thereof, and means governed by the intermittent operation of the timing relay.

Further features of the invention pertain to the particular arrangement of the circuit elements thereof, whereby the above-outlined and additional operating features are attained.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. rI"he invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings in which Figure 1 illustrates the general arrangement of a telephone system including a central exchange and a distant exchange and embodying the present invention; and Figs. 2 to 6, inclusive, taken together, illustrate the details of a system having incorporated therein the features of the invention, as briefly outlined above,

DESCRIPTION or* rnc APPARATUS INCORPORATED 1N THE SYSTEM Referring now more particularly to Fig. lof the drawings, the telephone system 'there illustratedoomprises a central exchange 2li, a distant' exchange 10, a rst group of one-way trunk 'lines extending from 'the distant exchange fi to the central exchange 20, including the trunk line 50, and a second group of one-way trunk lines extending from the centralexchange' 20 to the distant exchange 1i), including the'trunkv line Sil. The central exchange 2U is of the semi-automatic 'type serving a number of manual subscriber substations, including the subscriber substations C and D; A telephone line having a line circuit individually associated therewith extends to each 'subscriber substation'in the centralexchange 2t; the telephone lines 'M and'112 having `the line circuits 45 'and 46 respectively associated therewith extend to the subscriber substaions C and D, respectively. The distant exchange lll is of the semi-automatic type serving a number of manual subscriber substations, including thesubscribersubstations A` and B. A telephone linehaving a line circuit and anonnum'erical automatic Vswitch individually associated therewith extends to each subscriber substation' in the distant exchange' 10; the telephone lines V'H and 'i2 having the line circuits 'i5 and "it and the non-numerical automatic switches 18 `and T9 respectively associated therewith extend to the subscriber substations A and B, respectively.

Each trunk line in the first group' of` trunk lines extending from the distant exchange 10 to Lthe central exchange20 terminates in a trunk circuity in the distant exchange 'l0 and in aiselectorY repeater in the central exchange 20. For example, the'trunk line` 50 in the rst'group of trunk lines4 terminates in the trunkA circuit 80 in the distant exchange 10 and in the selector redistant exchange 'l0 terminates in a repeater in thecentral exchange 2U and in an incoming selector switch in the distant exchange 10. For example, the trunk line 60 in the second group 'of trunk lines terminates in the repeater 65 in the central exchange 2i] and inthe incoming selector switch in thek distant exchange 1i). Also the distant exchange 10 comprises a switch train'including, in addition to the group of non-.

numerical automatic switches and the group of incoming selector switches, a number of groups of connector switches, one of the groups of connector switches including the vconnector switch 95. Each non-numerical automatic switch has access'to each of the trunk circuits; each of the incoming selector switches has access to the connector switchesin the various groups of connector switches; while the connector switches in the various groups of connector switches have access to the various groups of telephone lines.

Also the central exchange 20 comprises, in addition to the group of selectorrepeaters and the groupy of repeaters, a local automatic switch train 2|, a switchboard provided with a number of operator positions including the rst operator position 30, a main master impulse generator 22, and an auxiliary master impulse generator 23. Preferably each operator position is identical to the rst operator position 3,0, which comprises operator telephone and control equipment 3|, operator connecting apparatus 32, and a key sender 33.

Each of the selector repeaters is accessible to each of the operator positions, thereby to allow the operator at any operator position to answer a call from the distant exchange to the central exchange 20 on the selector repeater. Furthermore, each selector repeater has access to each repeater and to the local automatic switch train 2|. The local automatic switch train 2| is accessible to each telephone line in the central exchange 20, and to each operator position, and has access to each operator position, to each telephone line in the central exchange 20 and to each of the repeaters. Finally, the main master impulse generator 22 and the auxiliary master impulse generator 23 are commonly associated with the repeaters and are operative to control the various repeaters and the key senders at the various operator positions, in a manner more fully explained hereinafter.

Each subscriber substation in the central exchange 20 and each subscriber substation in the distant exchange 10 is provided with substation equipment including a telephone instrument and a ringer. The line circuits individually associated with the telephone lines in both the central exchange 20 and the distant exchange 10 are of conventional connection and arrangement. Also the non-numerical automatic switches in the distant exchange 10 are of a conventional type; while the incoming selector switches and the connector switches in the distant exchange 10 are of the well-known Strowger type.l

Preferably, each of the trunk circuits in the distant exchange 10 is identical to the trunk circuit 80 which comprises, as best shown in Fig. 2, a number of relays including a line relay R220, a hold relay R230, a busy relay R240 and a bridge relay R250, connected and arranged in a manner more fully described subsequently.

Preferably, each of the selector repeaters in the central exchange 20 is identical to the selector repeater 55 which comprises, as best shown in Fig. 3, a switching mechanism 300 of the 100- point Strowger type, including a carriage provided with a wiper set including the wipers 30|, 302, 303 and 304, the wipers mentioned being capable of both vertical and rotary movements. Further the mechanism 300 comprises a circumferentially disposed main contact bank associated with the wiper set, the wiper set having access to a group of one hundred lines terminated by the main contact bank. Also the mechanism 300 is provided with a Vertical magnet M305 for moving the wiper set thereof in the vertial direction, a rotary magnet M301 for moving the wiper set thereof in the rotary direction, and a release magnet M309 for releasing the wiper set thereof and for causing the wiper set to lbe returned to its normal position. Finally the switching mechanism 300 has a number of switch springs S3|0, S3| I, S3|2, S3|3, S3|4, S3|5 and S3|8 operatively associated therewith, which are controlled in accordance with the movements of the wiper set thereof, in a manner more fully explained subsequently.

Also the selector repeater 55 comprises a number of relays including a line relay R325, two hold relays R330 and R360, a start relay R340, a send relay R345, an answer relay R350, an impulse relay R310, a control relay A315, a transfer relay R380 and a switching relay R390, connected and arranged in a manner more fully described subsequently.

in the associated group of repeaters.

Preferably, each of the repeaters in the central exchange 20 is identical to the repeater 65 which comprises, as best shown in Fig. 5, a repeater transformer 500 and a number of relays including a dial impulse relay R5I0, an answer relay R5l5, a control relay R520, a start relay R525, a revertive impulse relay R530, a digit relay R535, a pickup relay R540, a hold relay R550 and a timing relay R560, connected and arranged in a manner more fully described subsequently.

The local automatic switch train 2| is of a well-known type, including finder switches, selector switches and connector switches, each being of the all-relay type, wherein the selector switches and the connector switches are operative to transmit revertive control impulses, in a manner more fully explained subsequently.

Preferably, each operator position in the central exchange 20 is connected and arranged in a conventional manner, the operator telephone and control equipment 3|, the operator connecting apparatus 32 and the key sender 33 individually associated with the rst operator position 30 being of well-known types. More particularly, the operator telephone and control equipment 3| comprises a telephone instrument, not shown, and a number of control keys, not shown, for setting up and supervising connections at the rst operator position 30; the key sender 33 comprises a key set, not shown, and a number of registers including the first register 400; and the operator connecting apparatus 32 comprises a number of connect keys, individually associated with the trunks in a first group of trunks extending to the group of selector repeaters and a second group of trunks extending to the local automatic switch train 2|, and a number of supervisory lamps. For example, the connect key K440 in the operator connecting apparatus 32 is individually associated with the trunk 35 extending to the selector repeater 55 and has individually associated therewith a line lamp L441 and an answer lamp L44B; while the connect key K445 is individually associated with the trunk 34 extending to the local automatic switch train 2| and has individually associated therewith a line lamp and an answer lamp, not shown.

Preferably, both the main master impulse generator 22 and the auxiliary master impulse generator 23 in the central exchange 20 are identical and are commonly associated with each repeater As best shown in Fig. 6, the main master impulse generator 22 comprises two impulse relays R600 and R6|0, two cycle relays R620 and R630, a start relay R640, a timing relay R650, a lockout relay R350 and a hold relay R610, connected and arranged in a manner more fully described subsequently. Also the main master impulse generator 22 comprises an interrupter 1680, two supervistory lamps L6I1 and LBIB and a reset key K516. The master impulse generators 22 and 23 are so connected and arranged that the main master impulse generator 22 is normally operatively associated with the repeaters in the associated group of repeaters and is adapted, in the event of failure thereof, operatively to associate the auxiliary master impulse generator 23 with the repeaters in the associated group of repeaters.

A better understanding of the connection and arrangement of the telephone system will be facilitated from a consideration of the general operation of the various pieces of apparatus incorporated therein incident to the completion and handling of Various calls at the first operator position 39 in the central exchange 20, as will appear hereinafter.

General operation of the system operator position in the central exchange 2i! and then extended from the operator position to the various subscriber substations in both the central exchange and in the distant exchange lll. Y

For example, when a call is initiated at the subscriber substation C in the central exchange 29, the line circuit 45 individually associated with the telephone line 4| is controlled, thereby to cause the local automatic switch train 2| to opcrate and seize the telephone line 4| and an idle trunk, such as the trunk 34, extending to' the operator positions. When the trunk SLi-is thus seized, signals are transmitted to the various operator positions in the central exchange 20; whereupon the operator at one of the operator positions, such, for example, as the iirst operator position 30, answers the call by operating the connect key KMS in the operator connecting apparatus 32 individually associated with the trunk 34 and is advised concerning the extension of the call.

In the event the call is to be extended to another subscriber substation in the central exchange 23, such, for example, as the subscriber substation D, the operator at the rst operator position 39 then registers in the key sender 33 the appropriate digits in order to control the operation of the local automatic switch train 2|. The local automatic switch train 2| then operates to seize the telephone line 42 extending to the subscriber substation D. The subsequent operation of the local automatic switch train 2| depends upon the idle or busy condition of the` subscriber substation D in accordance with conventional practice. The operator at the rst operator position 39 then returns the connect key K45 in the operator connecting apparatus 32 back to its normal position, thereby to release the apparatus at the first operator position 39.

On the other hand, in the event the call is to be extended to a subscriber substation in the distant exchange lil, such, for example, as the subscriber substation B, the operator at the rst..

exchange 75 to extend the call to the subscriber ,y

substation B in the distant exchange I is explained more fully hereinafter. After operation oi the repeater 55 and the previously mentioned apparatus in the distant exchange 7|), the` operator at the first operator position 35 returns the f connect key KME in the operator connecting apparatus 32 back to its normal position, thereby to release the apparatus at the first operator position 30.

For example, when a call is initiated at the subscriber substation 'A in the distant exchange 70, the-line circuit 15 individually associated with the'telephone line is controlled, thereby to cause the non-numerical automatic switch 18 to seize an idle trunk in the group of trunksextending to the associated trunk circuits, such, for example, as the trunk 8| extending to the trunk circuit 80. When the trunk 8| is thus seized the trunk Vcircuit 80 operates, thereby to cause operation of the selector repeater by way of the associated trunk line 50, whereupon signals are transmitted to the various operator positions in the central exchange 2|). The operator at one of the operator positions, such, for example, as the rst operator position 30, answers the call by operating the connect key K440 in the operator connecting apparatus 32 individually associated with the trunk 35 extending to the selector repeater 55 and is advised concerning the extension of the call. l

In the event thel call is to be extended to a subscriber substation `in the central exchange 29, such, for example, as thesubscriber substation D, the yoperator at the first operator position 30 then'registers in the key sender 33 the appropriate digits in order to control the operation ofthe selector repeater 55 and the local automatic vswitch train 2 The local automatic switch train2 |l then operates to seize thetelephone line L12 extending to the subscriber substation D. The subsequent operation of the local automatic switch train 2| depends upon the idle or busy condition of the subscriber substation D, as previously noted. The operator at the first operator position 3|! then returns the connect key KMU in the operator connecting apparatus 32 back to its normal position, thereby to release the apparatus at the first operator position 3U.

On the other hand, in the event the call `is to ybe Vextended to a subscriber substation in the distant exchange 10, such, for example, as the subscriber substation B, the operator at the lirst operator position 13.0'then registers in the key sender 33 the appropriate digits in order to control Vthe operation of the, selector repeater 55, whereupon the selector repeater 55 operates to seize an idle .trunk'in the group of trunks extendingy lto the group of repeaters, such, for examp1e,as the trunk 31 extending to the Arepeater When the trunk 31 is thus seized the repeater operatesin orderto condition the incoming selector switch inthe distant exchange 10 by way of the associated trunk line-6|] and to initiate operation of the main master impulse generator 22, in the event it is not already operating. The main master impulse generator 22 causes impulses corresponding to the impulses registered in the various registers in the key sender 33 to be transmitted by way of the repeater 65 over the trunkline 6|) to the incoming selector switch 99, ythereby to cause operation of the incoming selector switch 90 and the succeeding connector switch. More particularly, the incoming selector switch 99 is operative to select an idle one of the connector switches in-one of the groups of connector switches, such, for example, as the connector switch 95. The connector switch is -then operated to seize the telephone line 12 extending to the subscriber substation B in the distant exchange l0. The subsequent operation of the connector switch 95 depends upon the idle or busy condition of the subscriber substation B vin accordance with conventional practice.

After the repeater 65 is thus operated, the operator at the rst operator position 30 returns the connect key K440 in the operator connecting apparatus 32 back to its normal position, thereby to release the apparatus at the iirst operator position 30. Y

It is noted that the release of an established connection between two subscriber substations in the central exchange 20, between two subscriber substations in the distant exchange 'l0 and between a subscriber substation in the central exchange 20 and a subscriber substation in the distant exchange is primarily under the control of the subscriber at the calling subscriber substation and is effected when the subscriber at the calling subscriber substation performs a release operation thereat.

Further it is noted that, in the event a false call is initiated on a telephone line in the distant exchange '10, such as the telephone line 1| extending to the subscriber substation A, the call is extended by way of one of the trunk lines, such as the trunk line 50, and the associated selector repeater 55 to one of the operator positions in the central exchange 20 to be answered. For example, the false call may be answered at the first operator position 30 in the manner previously explained. After the operator at the first operator position 30 determines that the call is a false call she operates the key sender 33, thereby to cause the selector repeater 55 to be operated in accordance with a single digit, in a manner more fully described hereinafter. When the selector repeater 55 is thus operated the line circuit 15 individually associated with the telephone line 1| is operated in order to lock the telephone line 1| out of service. The telephone line 1| remains locked out of service until the fault thereon is removed.

As previously noted, the main master limpulse generator 22 is operative to control each repeater in the associated group of repeaters and is so connected and arranged that, in the event it fails properly to operate, it operates subsequently, thereby to intiate operation of the auxiliary master impulse generator 23, whereby the auxiliary master impulse generator 23 ls rendered operative to control each repeater in the associated group of repeaters. Finally it is noted that both the main master impulse generator 22 and the auxiliary master impulse generator 23 are operative to control simultaneously a large number of repeaters in the associated group of repeaters, the repeaters in the associated group being divided into odd and even subgroups.

Detailed operation of the system A call from a subscriber substation in the distant exchange 10, such as the subscriber substation A, is rst initiated by removing the receiver of the telephone instrument thereat from its associated switchhook, thereby to cause operation of the line circuit individually associated with the telephone line 1| extending to the subscriber substation A. Upon operating, the line circuit 'l5 marks the telephone line 1| extending to the subscriber substation A as busy to the switches having access thereto and initiates operation of the non-numerical automatic switch 18 individually associated with the telephone line 7|, whereupon the non-numerical automatic switch 'I8 operates to seize an idle trunk accessible thereto, such as the trunk 8| extending to the trunk circuit 80, the trunk 8| being marked as idle by the absence of ground potential upon the control conductor C203 thereof. When the nonnurnerical automatic switch 18 seizes the trunk 8| a loop circuit is completed between the subscriber substation A and the line relay R220 in the trunk circuit 80, this circuit extending from ground by way of the lower winding of R 220 to the line conductor C202 of the trunk 8| and from battery by way of the upper winding of R220 to the line conductor C20| of the trunk 8|, the line conductors C20| and C202 of the trunk 8| being connected by Way of the non-numerical automatic switch T8 and the telephone line 1| to the subscriber substation A. When this loop circuit is completed the line relay R220 operates to interrupt, at the contacts 223, a circuit traced hereinafter for energizing the winding of the busy relay R240 to prepare, at the contacts 22|, a circuit traced hereinafter for energizing the Winding of the bridge relay R250 and to cornplete, at the contacts 224, a path for applying ground potential to the line conductor C2|| of the trunk line 50 extending between the trunk circuit in the distant exchange 10 and the selector repeater 55 in the central exchange 20. 'The path for applying ground potential to the line conductor C2| of the trunk line 50 extends from ground by way of the contacts 233 and. 224 to the line conductor C2|| of the trunk line 50.

The application of ground potential to the line conductor C2|| of the trunk line 50 completes a circuit for energizing the winding of the start relay R340 in the selector repeater 55, this circuit extending from the grounded line conductor C2|| of the trunk line 50 by way of the set of switch springs S3|0, the contacts 362 and the winding of R340 to battery. When thus energized the start relay R340 operates to complete, at the contacts 34|, a path for applying battery potential by way of the upper winding of the line relay R325 to the line conductor C2 0 of the trunk line 50, thereby to complete a circuit for energizing in series the upper winding of the line relay R325 in the selector repeater 55 and the winding of the bridge relay R250 in the trunk circuit 80. This circuit extends from ground by way of the contacts 233 and the winding of R250 to the contacts 22| and from' ground by way of the resistor 242 and the contacts 252 to the contacts 22| and from the contacts 22| by way of the line conductor C2|0 of the trunk line 50, the contacts 34| and 38| and the upper winding of R325 to battery. When thus energized the bridge relay R250 in the trunk circuit 80 and the line relay R325 in the selector repeater 55 operate.

Upon operating, the bridge relay R250 interrupts, at the contacts 252, the previously traced multiple path in the above-traced circuit, including the resistor 242, and completes, at thev contacts 253, an obvious circuit for energizing the winding of the hold relay R230. When thus energized the hold relay R230 operates to complete, at the contacts 234, an obvious path for applying ground potential to the control conductor C203 of the trunk 8|, thereby to mark the trunk 0| in the trunk circuit 80 as busy to the nonnumerical automatic switches having access thereto. Further the hold relay R230 interrupts, at the contacts 232, a further point in the previously mentioned circuit for energizing the winding of the busy relay R240 and interrupts, at the contacts 233, the previously traced circuit for energizing in series the winding of the bridge relay R250 in the trunk circuit 80 and the upper winding of the line relay R325 in the selector repeater 55, a loop circuit traced hereinafter M309 of the switching mechanism 300 and corn-v being completed at this time, including the winding of the bridge relay R250 inthe trunk circuit 80 and the upper and lower windings of the line relay R325 in the selector repeater 55. Finally the hold relay R230 completes, at the contacts 23|, a connection between the Iline conductor C202 of the trunk 8| and the line conductor C2|| of the trunk line 50. Accordingly, at this time, the line conductor C| of the trunk 8| is operatively connected by way of the condenser 225 and the contacts to the line conductor C2|6 of the trunk line while the line conductor C202 of the trunk 8| is operatively connected by way of the condenser 226 and the contacts 23| to the line conductor C2|| of the trunk line 53.

Upon operating, the line relay R325 in the selector repeater completes, at the contacts 326, the previously mentioned loop circuit for energizing in series the winding of the b-ridge relay R253 in the trunk circuit 80 and the upper and lower windings of the line relay R325 in the selector repeater 55, this circuit extending from ground by way of the set of switch springs S3 |3, the contacts 353 and 325, the lower winding of R325, C2i l, the contacts 224, the Winding of R250, the contacts 22|, C2l0, the contacts 34| and 38| and the upper winding of R325 tc battery. Also the line relay R325 completes, at the contacts 326, a series holding circuit for energizing the lower winding thereof and the winding ating, the hold relay R330 completes, at the contacts 333, an alternative loop circuit for energizing in series the winding of the bridge relay R250 in the trunk circuit 80 and the upper and lower windings of the line relay R325 in the selector repeater 55; and an alternative series circuit for energizing the lower winding of the line relay R325 and the winding of the start relay R340, these circuits extending from ground by way of the contacts 3|`| of the set of switch Springs S3l5, the contacts 333 and the lower winding of R325 to the line conductor C2|| of the trunk line 50; and therefrom, by Way of the previously traced circuits to battery at the upper winding of the line relay R325 and to battery at the winding of the start relay R340,

Also the hold relay R333 completes, at the contacts 332, a direct loop circuit for energizing in series the winding of the bridge relay R250 in the trunk circuit 80 and the upper and lower windings of the line relay R325 in the selector repeater 55, 'this circuit extending from ground by way of the set of switch springs S3|3 and the contacts 353 and 326 and from ground by way of the contacts 3|'l of the set of switch springs S3|5 and the contacts 333, by way of the lower winding of the line relay R325 to the line conductor C2|| of the trunk line 50, and therefrom by way of the previously traced path, including the winding of the bridge relay R250 in the trunk circuit 30 to the line conductor C250 of the trunk line 50, and 'therefrom by way of the contacts 332 and the upper winding of R325 to battery. Further the hold relay R330 interrupts, at the contacts 334, a point in a circuit traced hereinafter for energizing the release magnet pletes, at the contacts 336, a circuit for energizing the upper winding of the transfer relay R380, this circuit extending from ground by way of the contacts 336, 342 and the upper winding of R380 to battery. When thus energized the transfer relay R380 operates to prepare, at the contacts 384, a circuit traced hereinafter for energizing the Vertical magnet M305 of the switching mechanism 300 and to prepare, at the contacts 385, a circuit traced hereinafter for energizing the winding of the rotary magnet M301 of theV switching mechanism 300.

Further, the hold relay R330 completes, at the contacts 336, a path for applying ground potential to the control conductor C454 of the trunk 35 extending between the selector repeater 55 and the operator connecting apparatus at the various operator positions, this path extending from ground by way of the contacts 336, 343 and 355 'to the control conductor C454 of the trunk 35. The application of ground potential to the control conductor C454 of the trunk 35 completes obvious multiple circuits for illuminating the line lamps in the operator connecting apparatus at the various operator positions. For example, the line lamp L441 in the operator connecting apparatus 32- at the first operator position 30 is illuminated, thereby to indicate to the operator thereat that there is a call from the distant eX- change 10 on the selector repeater 55 waiting to be answered. Assuming that the call is answered at the first operator position 30, this is accomplished by operating the connect key K440 in the operator connecting apparatus 32 indi- Vidually associated with the trunk 35. When the connect key K440 is thus operated there is completed, at the contacts 443 thereof, an obvious path for applying battery potential by way of the cable 480 and the resistor 448 to the control conductor C453 of the trunk 35 and obvious multiple circuits for illuminating the answer lamps L446, etc., in the operator connecting apparatus 32, etc.. The illumination of the answer lamp L446, etc., in the operator connecting apparatus 32, etc., indicates to the operators at the various operator positions thatthe connect key in one operator connecting apparatus occupies its operated position, thereby to complete a connection between the selector repeater 55 and the associated operator position.

The application of battery potential to the control conductor C453 of the trunk 35 completes a circuit for energizing the winding of the answer relay R350, this circuit extending from ground by way of the contacts 336, 343 and the winding of R350 to battery potential upon the control conductor C453 of the trunk 35. When thus energized the answer relay R350 operates to interrupt, at the contacts 355, the previously traced circuits for illuminating the line lamps, L441, etc., in the operator connecting apparatus 32, etc., thereby to indicate to the operator at the first operator position 30 that the selector repeater 55 has been conditioned to be responsive to operation of the key sender 33, in a manner more fully explained hereinafter. Also when the connect key R440 in the operator connecting apparatus 32 is thus operated there is completed, at the contacts 44| and 442 thereof, an obvious connection between the line conductors C45! and C452 of the trunk 35 and the trunk conductors C43| and C432 at the rst operator position 30, both the operator telephone and control equipment 3| and the key sender 33 being directly Also, upon operating, the answer relay R350 completes, at the contacts 354, a circuit for energizing the winding of the hold relay R360, this circuit extending from ground by way of 'the set of switch springs S3I3, the contacts 354 and the winding of R360 to battery. When thus energized the hold relay R360 operates to interrupt, at the contacts 362, the previously traced holding circuit for energizing in series the lower winding of the line relay R325 and the winding of the start relay R340 and to complete, at the contacts 363, an alternative holding circuit for energizing the winding of the start relay R340. The last-mentioned circuit extends from ground by way of the contacts 336, 342 and 363 and the winding of R340 to battery. Accordingly, the start relay R340 remains in its operated position. Also the line relay R325 remains in its operated position due to the completed direct loop circuit including the winding of the bridge relay R250 in the trunk circuit 80 and the upper and lower windings of the line relay R325 in the selector repeater 55. Also the hold relay R360 prepares, at the contacts 36|, a circuit traced hereinafter for energizing the lower winding of the control relay R315 and prepares, at the contacts 364, a circuit traced hereinafter for energizing the winding of the impulse relay R310. Finally the answer relay R350 completes, at the contacts 352, an operative connection between the operator telephone and control equipment 3| at the first operator position 30 and the trunk line 50, this connection extending from the line conductor C2|0 of the trunk line 50 by way of the condenser 32|, the contacts 346, the line conductor C45| of the trunk 35, the contacts 44| of the connect key K440 and the trunk conductor C43| to the operator telephone and control equipment 3|; and from the line conductor C2! I of the trunk line 50 by way of the condenser 322, the contacts 352, the line conductor C452 of the trunk 35, the contacts 442 of the connect key K440 and the trunk conductor C432 to the operator telephone and control equipment 3|. As previously noted, the telephone instrument at the subscriber substation A is operatively connected by way of the telephone line 1|, the non-numerical automatic switch 10, the trunk 8| and the trunk circuit 80 to the trunk line 50 at this time; while the trunk line 50 is operatively connected by way of the selector repeater 55, the trunk 35 and the connect key K440 to the operator telephone and control equipment 3| at this time. Accordingly, the telephone instrument at the subscriber substation A in the distant exchange 10 is operatively connected to the operator telephone and control equipment 3| at the rst operator position 30 in the central exchange 20, whereupon the subscriber at the subscriber substation A and the operator at the rst operator position 30 communicate with each other, the operator at the first operator position 30 being advised concerning the extension of the call.

After answering the call on the trunk line 50, the operator at the first operator position 30 may extend the call to any subscriber substation in the central exchange 20 or to any subscriber substation in the distant exchange 10. Assuming that the call is to be extended to a subscriber substation in the central exchange 20, such as the subscriber substation D, the operator at the first operator position 30 initiates the extension of the call by operating the key sender 33, therebridged across the trunk conductors C43I and by to cause a number of digits to be registered in the several registers included therein and corresponding to the switch train route, including the selector repeater 55 and the local automatic switch train 2|, to the telephone line 42 extending to the subscriber substation D. More particularly, the rst digit is registered in the first register 400 in the key sender 33; whereupon the register switch S4|0 therein is operated away from its normal position and the digit switch S420 therein is set such that it is operated away from its normal position when a predetermined number of impulses corresponding to the digit registered in the first register 400 have been transmitted over the trunk 35 to the selector repeater 55. Similarly, the second, third, etc., digits are registered in the second, third, etc., registers in the key sender 33. When the register switch S4|0 in the iirst register 400 in the key sender 33 is operated away from its normal position, there is completed a path for applying ground potential in the rst register 400 t0 the line conductor C452 of the trunk 35, this path extending from ground by Way of the contacts 424 of the digit switch S420 in the first register 400, the contacts 4|2 of the register switch S4|0 in the first register 400, the trunk conductor C432 and the contacts 442 of the connect key K440 to the line conductor C452 of the trunk 35. This application of ground potential to the line conductor C452 of the trunk 35 completes an obvious circuit for energizing the winding of the send relay R345 in the selector repeater 55, thereby to cause operation of the send relay R345. Upon operating, the send relay R345 completes, at the contacts 348, an obvious holding circuit for eriergizing the winding of the answer relay R350 and completes, at the contacts 341, the previously mentioned circuit for energizing the lower winding of the control relay R315. The circuit for energizing the lower winding of the control relay R315 extends from ground by way of the contacts 341, 36|, 31| and 308 and the lower winding of R315 to battery. When thus energized the control relay R315 operates to complete, at the contacts 316, a holding circuit for energizing the lower winding thereof, this circuit extending from ground by way of the contacts 341, 316 and 308 and the lower winding of R315 to battery. Further the control relay R315 completes, at the contacts 311, a circuit for energizing in series the winding of the impulse relay R310 in the selector repeater 55 and the register magnet M425 in the iirst register 400 in the key sender 33, this circuit extending from ground by way of the contacts 311 and 364, the winding of R310, the contacts 33|, the line conductor C45| of the trunk 35, the contacts 44| of the connect key X440, the trunk conductor C43l, the contacts 4| of the register switch S4I0 in the first register 400, the contacts 42| of the digit switch S420 in the first register 400 and the winding of M425 to battery. When this circuit is completed the impulse relay R310 and the register magnet M425 operate.

Upon operating, the register magnet M425 in the first register 400 operates the associated pawl 426, thereby to condition the associated ratchet wheel 421 to be driven one step in the clockwise direction. Upon operating, the impulse relay R310 completes, at the contacts 313, an obvious holding circuit for energizing the winding of the hold relay R360 and completes, at the contacts 312, a circuit for energizing the Vertical magnet M305, this circuit extending from ground by Way of the contacts 341, 316, 312 and 384 and the' vertical magnet M305 to battery. When thus energized the vertical magnet M305 operates to drive the wiper set of the switching mechanism 300- one step in the vertical direction and to complete, at the contacts 306,- a circuit for energizing the upper winding ofthe -control relay R315, this circuit extending from ground by way of the contacts 341, 316 and 306 and the upper winding of R315 to battery. When both the upper winding and the lower winding of the control relay R315 are thus energized this relay restores, the control relay R315 being of the differential type. Upon restoring, the control relay R315 interrupts, at the contacts 311, the previously traced series circuit for energizing the winding of the impulse relay R310 in the selector repeater 55 and the register magnet M425 in the rst register 400, thereby to cause the impulse relay R310 and the register magnet M425 to restore.

Upon restoring, the register magnet M425 in the rst register 400 releases the associated pawl 426, thereby to cause the pawl 426 to drive the associated ratchety wheel 421 one step in the clockwise direction, thereby to effect registration of one impulse in the rst register 400. Upon restoring the impulse relay R310 interrupts, atr the contacts 312, the previously traced circuit.` for energizing the vertical magnet M305, u

thereby to cause the vertical magnet to restore. Upon restoring, the vertical` magnet M305 interrupts, at the contacts 306, the -previously traced circuit for energizing the upper winding of the -control relay R315. the control relay R315 interrupts, at the contacts 316, the previously traced holding circuit for energizing the lower winding thereof. Finally, upon restoring, the impulse relay R310 recompletes, at the contacts 31|, the previously traced original circuit for energizing the lower winding ofthe control relay R315.

Accordingly, the control relay R315 reoperates, thereby to recomplete, at the contacts 311, the previously traced series circuit for energizing the winding of the impulse relay R310 in the selector repeater 55 and the register magnet M425-in the iirst register 400 in the key sender 33, whereupon the impulse relay R310 and the register magnet M425 reoperate. Upon reoperating, the control relay R315 recompletes, at the contacts 316, the previously traced holding circuit for. energizing the lower winding thereof; and upon operating, the impulse relay R310 reco-mpletes, at the contacts 312, the previously tracedcircuit for energizing the vertical magnet M305, thereby to cause the vertical magnet M305 to reoperate. Upon reoperating, the vertical magnet M305 recompletes, at the contacts 306,` the previously traced circuit for energizing the upper winding of the control relay R315, thereby to cause the latter relay to restore.

Accordingly, the impulse relay R310, the control relay R315 and the vertical magnet M305 interact in the above-described manner, thereby to cause the vertical magnet M305 to drive the wiper set of the switching mechanism 300 step by step in the vertical direction and to cause the register magnet M425 to drive the associated ratchet wheel 421 step by step in the clockwise direction. When the wiper set of the switching mechanism 300 has been driven in the vertical direction a number of steps corresponding to the impulses of the digit registered in the rst register 400 in the key sender 33, the ratchet Also, upon restoring,

wheel, 421 is drivenk a corresponding number. of steps in the clockwise direction, thereby to cause thel digit switch S420 inthe liirst register 400 to be operated away from -its normal position. When the digit switch S420 in the rstl register 400 is operated away from its normal position there is. completed, at the contacts 423 thereof, a path substantially identical to that previously traced for applying ground potential in the second register by way of the control conductor C416 extending theretov to the line conductor C452 of the trunk 35, thereby to retain completed the previously mentioned circuity for energizing the winding of the -send relay R345 in the selector repeater 55. 424 of the register switch S420 in the rst reg'- ister 400, there is interruptedA the previously traced path for applying ground potential in the rst register 400 to the line conductor C452 of the trunk 35. Accordingly, the send relay R345 in the selector repeater 55 remains in its op'erated position at this time; Further, at the contacts 42| ofthe register switch S420 in the rst register` 400, there is interrupted the previously traced path for applying battery potential by way of the register magnet M425 in the rst register 400 to the line conductor C45! of the trunk 35; and there is prepared, at the contacts 422 of the register switch S420 in the first register 400,

a path substantially identical to that previously traced for applying battery potential by way of Vthe register magnet in the second register in the key sender 33 and the control conductor C415 extending thereto to the line conductorv C45! of the trunk 35. At this point it is noted that there is a delay in the application oiv battery potential by way of the register magnet in the second register in the key sender 33A to thev control. conductor C415 and consequently to the line conductor C45! of the trunk 35. Accordingly, when the control relay R315 reoperates in'- cident to the restoration of the impulse' relay R310 and the vertical magnet M305, the impulse relay R310 doesV not immediately operate as the previously mentioned circuit for energizing in series the winding of the impulse relay R310 and the register magnet in the second register in the key sender 33- is not immediately completed. This delay is produced in the second register in the key sender 33 in order to allow the switching mechanism 300- in the selector repeater 55 adequate time to operate automatically and seize an idle trunk inthe previously selected group of trunks, in a manner more fully explained subsequently.

At this point it is notedv that, when the wiper set-of the switching mechanism 300 is driven one stepk in the vertical direction, the sets of switch springs S310 and S313 are actuated into disengagement and the sets of switch springs S3I I and S3I2 are actuated into engagement. Whenv the set of switch springs S3ll is actuated into engagement, a path traced hereinafter is prepared for applying ground potential to the line conduce tor C2401v ofthe trunk line 50; and when the set of switch springs S312 is actuated into engagement, a further point in the previously mentioned circuit for energizing the release magnet M309 is prepared. When the set of switch springs S310 is actuated into disengagement, a further point in the previously traced original circuit for energizing the winding of the start relay R340- is interrupted, the start relay R340 being retained inA itsv operated position at this timek due to thelcompleted holding circuit for en- Also, at the cont-actsl ergizing the winding thereof under the control of the operated hold relay R360. When the set of switch springs S3I3 is actuated into disengagement the previously traced original circuit for energizing `the winding of the hold relay R360 is interrupted, the hold relay R360 being retained in its operated position at this time due to the intermittent completion of the previously traced holding circuit for energizing the winding thereof Iunder the control of the impulse relay R310, the

hold relay R360 being of the slow-to-release type. Accordingly, the start relay R340 remains in its operated position, while the hold relay R360 remains in its operated position as long as the impulse relay R310 is intermittently operated. However, after the digit switch S420 in the first register 400 in the key sender 33 is operated as previously explained, battery potential is not immediately connected in the second register in the key sender 33 to the line conductor C45I of the trunk 35. Accordingly, the impulse relay R310 remains in its restored position following the complete operation of the wiper set of the switching mechanism 300 in the vertical direction.

Hence, shortly after the impulse relay R310 restores to interrupt, at the contacts 313, the previously mentioned holding circuit for energizing the winding of the hold relay R360, the latter relay restores. Upon restoring, the hold relay R360 interrupts, at the contacts 363, the previously traced holding circuit for energizing the winding of the start relay R340, thereby to cause the latter relay to restore shortly thereafter, the start relay R340 being of the slow-to-release type.

Upon restoring, the start relay R340 interrupts,

at the contacts 34|, the original loop circuit for `energizing in series the winding of the bridge relay R250 in the trunk circuit 80 and the upper and lower windings of the line relay R325 in the selector repeater 55; however, the last-mentioned relays do not restore at this time due to the previously traced completed alternative loop circuit for energizing the windings thereof. Further the start relay R340 interrupts, at the contacts 342, a further point in the previously traced holding circuit for energizing the winding thereof and interrupts, at the contacts 342, the previously traced circuit for energizing the upper winding of the transfer relay R380. However, the transfer relay R300 does not immediately restore, this relay being of the slow-to-release type. Also the start relay R340 interrupts, at the contacts 343, the previously traced original circuit for energizing the winding of the answer relay R350, the latter relay remaining in its operated position at this time due to the completed holding circuit for energizing the winding thereof. Finally, the start relay R340 prepares, at the contacts 344, a test circuit traced hereinafter for energizing the winding of the switching relay R390.

Also, upon restoring, the hold relay R360 interrupts, at the contacts 364, a further point in the previously traced circuit for energizing the winding of the impulse relay R310 and completes, at the contacts 365, a holding circuit for energizing the lower winding of the transfer relay R380 and a circuit for energizing the rotary magnet M301, the control relay R315 occupying its operated position at this time. These circuits extend from ground by way of the contacts 311 and 365 to the contacts 385 and from the contacts 385 by way of the lower winding of R380 to battery, and from the contacts 385 by way of the rotary magnet M301 to battery. When the lower winding of the transfer relay R380 is thus energized this relay remains in its operated position; and when the rotary magnet M301 is thus energized it operates to drive the wiper set of the switching mechanism 300 one step in the rotary direction and to interrupt, at the contacts 308, the previously traced circuit for energizing the lower winding of the control relay R315, thereby to cause the latter relay to restore. Upon restoring, the control relay R315 interrupts, at the contacts 311, the previously traced holding circuit for energizing the lower winding of the transfer relay R380 and the previously traced circuit for energizing the rotary magnet M301. When these circuits are interrupted the transfer relay R380 remains in its operated position, this relay being of the slow-to-release type; while the rotary magnet M301 restores to recomplete, at the contacts 308, a test connection between the control wiper 303 of the wiper set of the switching mechanism 30D and the lower winding of the control relay R315.

At this time, the wiper set of the switching mechanism 300 engages the contact set in the associated contact bank terminating the rst trunk in the associated group of trunks extending to the local automatic switch train 2l. In the event the first trunk mentioned is busy, ground potential appears upon the control conductor thereof, thereby to complete a circuit for energizing the lower winding of the control relay R315 and a path for short-circuiting the winding of the switching relay R390. The circuit for energizing the lower winding of the control relay R315 extends from the grounded control conductor of the trunk mentioned by way of the control wiper 303, the contacts 394, 382 and 308 and the lower winding of R315 to battery; while the path for short-circuiting the winding of the switching relay R390 extends from the grounded control wiper 303 by way of the contacts 394 and 362, the Winding of R390, the contacts 3I9 of the set of switch springs S3|8, the contacts 344 and 336 to ground. Accordingly, in the event the trunk mentioned is busy, the control relay R315 reoperates while the switching relay R390 remains in its restored position. Upon reoperating, the control relay R315 recompletes, at the contacts 311, the previously traced holding circuit for energizing the lower winding of the transfer relay R380 and the previously traced circuit for energizing the rotary magnet M301, thereby to retain the transfer relay R380 in its operated position and to cause reoperation of the rotary magnet M301. Accordingly, the control relay R315 and the rotary magnet M301 interact in the manner described above, thereby to cause the wiper set of the switching mechanism 300 to be driven step by step in the rotary direction until it selects an idle trunk in the group of trunks extending to the local automatic switch train2l.

When an idle trunk in the group of trunks extending to the local automatic switch train 2i is thus selected, further operation of the rotary magnet M301 is arrested due to the absence of ground potential upon the control conductor thereof. More particularly, when no ground potential is applied to the control wiper 303 the previously traced circuit for energizing the lower winding of the control relay R315 is not recompleted and the previously traced path for shortcircuiting the winding of the switching relay R390 is interrupted. Hence, at this time, a circuit is completed for energizing in series the lower winding of the control relay R315 and the 'winding of the switching relay R390, this circuit extending from ground by way of the contacts 336 fand 344, the contacts 3|9 of the set of switch springs 1S3|8, the windings of R390, thecontacts y308 and the lower winding of R315 to battery. When this series circuit is completed the switchingrelay R300 operates; however, the control relay-R315 does not reoperate due to the high series resistance Yof this circuit. Upon operating, the lswitching relay R390 completes, at the contacts 395 and 396, obvious paths for applying ground potential to lthe control wipers 303 `and 304, respectively, thereby to cause ground potential to be applied to theY two control conductors of the selected trunk in the group of trunks extending to the local switch train 2|, such as the trunk 36. Also, upon operating, the switching relay R390 interrupts, vat the contacts 39|, a furtherY point in the previously traced circuit for energizing the winding of the impulse relay R310, 'and prepares, at the contacts 392 and 393, operative connections between the line conductors C2|0 and C2|| of the trunk line 50 and the line conductors C41| and C412, respectively, of the trunk 39. Finally, the switching relay R390 completes,l at the contacts 392, an operative connection between the line conductors C41| of the trunk 36 extending to the local automatic switch train 2| and the line conductor C45| of the trunk 35 extending to the key sender 33, for a purpose more lfully explained hereinafter. Shortly following the operation of the control relay R315 the transfer relay R380 restores, thereby to interrupt, at the contacts 385, a further point in the previously tracedholding circuit for energizing the lower winding of the transfer relay R380 and a vfurther point in the previously traced circuit for energizing the rotary magnet M301.

Accordingly, at this time, the selector repeater 55 has operated in response to the rst digit registered in the rst register 400 in the key sender 33 to select a group of trunks extending to the localautomatic switch train 2| and has then operated automatically to select the idle trunk 36 in the .previously mentioned group of trunks extending to the local automatic switch train 2 When ground potential is applied to the control conductors C413 and C414 of the trunk 36, the local automatic switch train 2| is rendered responsive to additional digits registered in the additional registers in the key sender 33 to operate subsequently. Shortly following the complete operation of the selector repeater 55 the second register in the key sender 33 operates, thereby to cause battery potential to be applied by way of the register magnet therein to the control conductor C415 extending thereto and, accordingly, by way of the previously traced circuit to the line conductor C45| of the trunk 35. The application of battery potential to the line conductor C45| of the trunk 35 completes an obvious path, including the line wiper 30| of the wiper set of the switching mechanism 300, for applying battery potential to the line conductor C41| of theft'runk 36 extending to the local automatic switch train 2|. This application of battery potential to the line conductor. C41| of the trunk 36 initiates operation of the local automatic switch train 2| whereupon the local automatic switch train 2| responds to the digit registered in the second register in the key sender 33and causes revertive impulses to be returned to the second'register in the key sender 33, thereby to control the transfer-of the circuit from the second register tolthe third register in thekey trunk 35.

sender 33, in a manner similar to the transfer of the connection from the iirst register 400 to the second register in the key sender.33, previously explained. Accordingly, the local automatic switch train 2| operates in accordance with the second, third, etc., digits registered in the second, third,-etc., registers in the key sender 33, thereby to Seize the telephone line 42 extending to the subscriber substation D. The subsequent operation of the local automatic switch train 2| depends upon the idle or busy condition of the telephone line 42, in a manner more fully explained hereinafter.

After all of the digits registered in the various registers in the key sender 33 have been transmitted by way of the trunk 35, the selector repeater 55 and the trunk 36 to the local automatic switch train 2| in order to cause operation thereof to seize the telephone line 42 extending to the subscriber substation D in the manner previously explained, the last register in the key sender 33 operates, thereby to cause ground and battery potential to be removed from the line conductors C452 and 045|, respectively, of the When battery potential is `removed. from the line conductor 045| of the trunk 35, further operation of the local automatic switch train 2| is arrested; and when ground potential is removed from the line conductor C452 of the trunk 35 the previously traced circuit for energizing the winding `of the send relay R345 is interrupted, thereby to cause the latter relay to restore. Upon restoring, the send relay vR345 completes, at the contacts 346, a connection traced hereinafter between the 'line conductor C2|0 of the trunk line 50 and the line `conductor C41| of the trunk 36, and interrupts, at the contacts 348, the previously traced holding circuit for energizing the winding of the answer relay R350, thereby to cause the latter relay to restore and complete, at the contacts 35|, a-connection between the line conductor C2|| of the trunk line 50 and the line conductor C412 of the trunk 36. At this time, the line conductor C2|0 of the trunk line 50 is connected by way of the condenser 32|, the contacts 346 and 392 and the line wiper 30| to the line conductor C41| of the trunk 36,' and the line conductor C2|| of the trunk line 50 is connected by way of the condenser 322, the contacts 35| and 393 and the line wiper 302 to the line conductor C412 of the trunk 36; the trunk line 50 lbeing connected by way of the trunk circuit 80, the trunk 8|, the non-numerical automatic switch 18 and the telephone line 1| to the subscriber sub-station A in the distant exchange 10 and the trunk 36 being connected to the local automatic Switch train 2|. Also, when the previously tracedholding circuit for energizing the winding of the answer relay R350 is interrupted, at the contacts 343, due to the restoration of the send relay R345, the re-v sistor 446 included in the previously traced circuit for illuminating the answer lamp L446 in the operator connecting apparatus 32 at the first operator position 30 is unloaded somewhat, thereby to cause the answer lamp D446 to be illuminated more brightly. When the answer lamp L446 is thus illuminated more brightly, it indicates to the operator at the first operator position 30 that the key sender 33 has been released. The operator at the operator position 30 then returns the connect key K440 in the operating .connecting apparatus 32 to its normal position, thereby to interrupt, at the contacts 44| and442 thereof, the connection between -both the operator ltelephone and control equipment 3| and the key sender 33 and the trunk 35 extending to the selector repeater 55 and to render the first operator position 30 again idle. Also when the connect key K440 is returned to its normal position there is interrupted, at the contacts 443 thereof, the previously traced multiple circuits for illuminating the answer lamps L446, etc., included in the operator connecting apparatus 32, etc., at the various operator positions, thereby to indicate to the operator at the rst operator position 30 that the apparatus thereat is idle and available for use in answering another call. f

In the event the called subscriber substation D in the central exchange 20 is busy at this time, the local automatic switch train 2| operates to return busy tone current over the previously traced connection to the subscriber substation A in the distant exchange 10, thereby to indicate to the subscriber thereat that the connection cannot be immediately completed due to the busy condition of the called subscriber substation D. One the other hand, in the event the called subscriber substation D is idle at this time, the local automatic switch train 2| operates to cause ringing current to be projected over the telephone line 42 to the called subscriber substation D and to cause ring-back tone current to be returned over the previously traced connection to the calling subscriber substation A, thereby to indicate to the subscriber at the subscriber substation A that the called subscriber substation D in the central exchange 20 is being rung. Also when the local automatic switch train 2| seizes the telephone line 42 extending to the called subscriber substation D, the line circuit 46 individually associated therewith operates, thereby to mark the telephone line 42 as busy to the switches in the local automatic switch train 2| having access thereto. When the subscriber at the called subscriber substation D answers the call the local automatic switch train 2| switches through, thereby to complete a connection between the trunk 36 and the telephone line 42, in order to complete an established connection between the calling subscriber substation A in the distant exchange and the called subscriber substation D in the central exchange 20.

In the foregoing explanation of the mode of operation of the selector repeater 55 it was assumed that there was an idle trunk in the previously selected group of trunks extending to the local automatic switch train 2| and that the selector repeater 55 seized the idle trunk in this group of trunks incident to the operation of the switching mechanism 300 thereof in the rotary direction. However, it may occur that there are no idle trunks in the previously selected group of idle trunks extending to the local automatic switch train 2|; in which event the control relay R315 and the rotary magnet M301 continue to operate in the manner previously explained, in order to drive the wiper set of the mechanism 300 step by step in the rotary direction until the wiper set is driven eleven steps away from its normal position. When the wiper set of the switching mechanism 300 is driven eleven steps away from its normal position the sets of switch springs S3| 5 and S3|8 are operated. More particularly, the contacts 3|9 of the set of switch springs S3 I8 vare actuated into disengagement; while the contacts 320 of the set of switch springs S3|8 are actuated into engagement, thereby to complete an alternative holding circuit for energizing the winding of the hold relay R360. This circuit extends from ground by way of the contacts 336 and 344, the contacts 320 of the set of switch springs S318 and the winding of R360 to battery. When thus energized the hold relay R360 operates and completes, at the contacts 36|, the previously traced circuit for energizing the lower winding of the control relay R315, thereby to cause the latter relay to operate. Upon operating, the control relay R315 completes, at the contacts 311, the previously traced series circuit for energizing the winding of the impulse relay R310 in the selector repeater 55 and the winding of the register magnet in the second register in the key sender 33, thereby to cause the impulse relay R310 and the register magnet mentioned to operate. Also upon operating, the control relay R315 completes, at the contacts 316, the previously traced holding circuit for energizing the lower winding thereof. Upon operating,the impulse relay R310 completes, at the contacts 312, an alternative circuit for energizing the upper winding of the control relay R315, this circuit extending from ground by way of the contacts 341, 316, 312 and 383 and the upper winding of R315 to battery. When both the upper winding and the lower winding of the control relay R315 are thus energized, this relay restores as it is of the differential type, as previously noted. Upon restoring, the control relay R315 interrupts, at the contacts 316, the previously traced holding circuit for energizing the lower winding thereof and interrupts, at the contacts 311, the previously traced 'circuit for energizing the winding of the impulse relay R310, thereby to cause the latter relay to restore. Upon restoring, the impulse relay R310 interrupts, at the contacts 312, the previously traced alternative circuit for energizing the upper winding of the control relay R315 and recompletes, at the contacts 31|, the previously traced original circuit for energizing the lower winding of the control relay R315. Accordingly, the impulse relay R316 and the control relay R315 interact in the above-described manner in order to cause all the digits registered in the second, third, etc., registers in the key sender 33 to be transmitted, whereby the registers mentioned in the key sender 33 are completely cleared, in the manner previously described, the same as though the selector repeater 55 had switched through to seize the local automatic switch train 2| in the manner previously explained.

When the set of switch springs S3| 5 is thus actuated the previously traced alternative loop circuit, including the winding of the bridge relay R250 in the trunk circuit and the upper and lower windings of the line relay R325 in the selector repeater 55, is interrupted at the contacts 3|1 thereof; and, at the contacts 3|6 of the set of switch springs S3I5, there is completed a further loop circuit including the winding of the bridge relay R250 in the trunk circuit 80 and the upper and lower windings of the line relay R325 in the selector repeater 55. This further loop circuit extends from ground by way of the winding of a busy tone transformer, not shown, the set of switch springs S3|4, the conta/cts 3|6 of the set of switch springs S3l5, the contacts 333, the lower winding of R325, C2||, the contacts 224, the winding of R250, the contacts 22|, C2|0, the contacts 332 and the upper winding of R325 to battery. Accordingly, busy tone current traverses the previously traced further loop circuit, thereby to cause busy tone current to be projected from the trunk circuit 80 over the trunk 8|, the

non-numerical automatic switch 18 and the telephone line 1l to the subscriber substation A in the distant exchange in order tov cause the receivery of the telephone instrument at the subscriber substation A to produce busy tone. The subscriber at the calling subscriber substation A then effects the release of the selector repeater 55 by replacing the receiver of the telephone instrument at the subscriber substation A upon its associated switchhook.

-At this point it is noted that the release of the selector repeater 55, in the event it fails to nd an idle trunk in the previously selected group ofv trunks extending to the local automatic switch train 2|, in the manner described above, and the release of the established connection between the calling subscriber substation A in the distant exchange 10 and the called subscriber substation D in the `central exchange 20 are performed in an, identical manner under the control of the subscriber at the calling subscriber substation A. More particularly, when the subscriber at the calling subscriber substation A in the distant exchange 10 replaces the receiver of the telephone instrument thereat upon its associated switchhook the loop circuit between the line relay R220 in the trunk circuit 80 and the subscriber substation A is interrupted, thereby to cause the latter relay to restore; also the line circuit individually associated with the telephone line 1I extending to the subscriber substation A is controlled, thereby to initiate operation of the non-numerical automatic switch 18 individually associated with the telephone line 1| extending to the subscriber substation A. More particu- 9 larly, the non-numerical automatic switch 18 is voperated to its normal position, whereupon the Aline circuit 15 is controlled, thereby to mark the telephone line 1| extending to the subscriber substation A as idle to the switches having access thereto.

Upon restoring, the line relay R220 interrupts, at the contacts 224, the previously traced series loop circuit, including the winding of the bridge relays R250 in the trunk circuit 80, and the upper and lower windings of the line relay R325 in the selector repeater 55, thereby to cause the latter relays torestore. Upon restoring, the bridge relay R250 interrupts, at the' contacts 253,

the previously mentioned circuit for energizing H the winding of the holdrelay R230, thereby to cause the latter relay to restore shortly thereafter, the hold'relay R230 being of the slow-torelease type. Upon'restoring, the hold relay R233 interrupts, at the `contacts 234, the previously mentioned path for applying ground potential to the control conductor C203 of the trunk 3l, thereby to mark the trunk 3| and the trunk circuit 80 as idle to the non-numerical automatic switches 'having access thereto. Upon restoring, `the line relay R325 interrupts, at the contacts 321, `the previously mentioned circuit for energizin'gthe winding of the hold relay R330, thereby to .cause the latter relay to restore shortly thereafter, the hold relay R330 being of the slow-torelease type. Upon restoring, the hold relay R330 completes, at the contacts 333, the previously mentioned circuit for energizing the release magnet M333, this circuit extending from ground by way of the contacts 334, the set of switch springs SM2 and the release magnet M339 to battery. When thus lenergized the release magnet M339 operates, thereby to release the `'wiperset of the switching mechanism 300 inv (ill order to cause this wiper set to be .returned to its normal position. When the-Wiper set of the switching mechanism 300 is returned to its normal position, the sets of switch springs S310 and S313 are actuated into engagement; the sets-of switch springs S3!! andS3l2 areactuated into disengagement; while thesets of switch springs S3l5 and S3I8 are actuated only in theevent they have been previously actuated due to the failure of the selector repeater 55 to seize an idle'v trunk in the previously-selected group of trunks extending to the local automatic switchtrain 2 I.

Assuming that the present release is eected incident to .the failure of the selector repeater 55 to seize a trunkin the previously selected group of trunks extending to the local automatic switch train 2l, the contacts 3|6 and 3I1 of the setof switch springs S3 l 5 are respectively actuated into disengagement and intoengagement; while the contacts 3|9 and i320 of the set of switch springs S3 f8 are actuated 'respectively into engagement and disengagement.Y Also upon restoring, the hold relay R330 interrupts, vat the contacts 333, a further point in the previously traced path for projectingbusy tone current over the trunk line and interrupts, at the contacts 336,r the previously traced alternative holding circuit for f energizing the winding of the hold relay R360. At' this point it is noted that the hold relay R350 does not immediately restore, this relay being of the slow-to-release type, and is retained in its operated position as long as the impulse relay R310 and the control relay R315 are interacting,v

inthe manner previously` explained, vthereby to clear the various registers in the key sender 33; alsov until the'registers in the key sender 33 are cleared the send relay R345 andthe answer relay R350 remain in their*operatedpositions. After the registers in the key, sender 33 have been cleared; thef'previously traced circuitfor 'energizing the send relay "R345 is interrupted, thereby to cause the latter relay to restore and interrupt, at the contacts 338, the previously traced circuit for energizing the answer relay R350, whereupon v the latter relayresto'res as previously explained. Also upon restoringthe sendr relay R345 interrupts, at the contacts 341, the previously traced circuit for energizingv the lower'winding of the control relay R315, thereby to cause the latter relay to restore and interrupt, at the contacts 311, a further point in .the` previously traced "circuit for energizing the winding of the impulse relay R310, whereby both the control relay R315 and the impulse'relayRSlO occupy their restored positions. Shortly after the impulse relay R310 restores to interrupt,.at the contacts 313, the previously mentioned alternative 1Aholding circuitfor energizing the winding of the hold relay R350, the hold relay R330, be,.-

ing of the slow-'to-release type, restores. At this time, the selector repeater is completely released and available for further use.

On the other hand, assuming -that the present "release is effected subsequent to the establishment of the completed connection between the calling subscriber substation A in the distant exchange 1.0 and the called subscriber substation D in the set 'of the switching mechanism 300 to be released and .returned to its normal position, in the manner previously explained. Also the sets of switch springs YSSID, S3I3andS3ll, S3|2 are respectively actuated into engagement and disengagement, as previously explained. Further in the present release, the hold relay R330 interrupts,v

at the c ontacts 336, the previously traced circuit for energizing the winding of the switching relay R390 in series with the lower winding of the control relay R315, thereby to cause the switching relay R390 to restore. Upon restoring, the switching relay R390 interrupts, at the contacts 392 and 393, the previously` traced connection between the selector repeater 55 and the trunk 36 extending to the local automatic switch train 2| and interrupts, at the contacts 395, the previously traced path for applying ground potential to the control conductor C413 of the trunk 36, the path for applying ground potential to the control conductor C414 of the trunk 36 being interrupted at the contacts 321 incident to the restoration of the line relay R325. At this time, the selector repeater 55 is completely released and available for further use. When ground potential is removed from the control conductors C413 and C414 of the trunk 36 extending to the local automatic switch train 2|, the local automatic switch train 2| is released and rendered available for further use. At this time, when the local automatic switch train 2| is released the line circuit 46 individually associated with the telephone line 42 extending to the called subscriber substation D in the central exchange is controlled, thereby to mark the telephone line 42 as idle to the switches in the local automatic switch train 2| having access thereto in the event the subscriber at the called subscriber substation D has replaced the receiver of the telephone instrument thereat upon its associated switchhook at this time, or to lock the telephone line 42 out of service in the event the subscriber at the called subscriber substation D has not replaced the receiver of the telephone instrument thereat upon its associated switchhook at this time.

In connection with the release of the selector repeater 55 it is noted that, in the event the wiper set of the switching mechanism 300 is not completely released and actually returned to its normal position incident to the restoration of the hold relay R330, a path is completed, at the contacts 33|, upon restoration of the hold relay R330 to apply ground potential to the line conductor C2|0 of the trunk line 50, this path extending from ground by way of the set of switch springs 53| and the contacts 33| to the line conductor C2| 0 of the trunk line 50. Accordingly, ground potential is retained upon the line conductor C2|0 of the trunk line 50 until the wiper set of the switching mechanism 300 is actually returned to its normal position, thereby to actu- `ate the set of switch springs S3| into disengagement. The application of ground potential to the line conductor C2|0 completes a circuit for energizing the winding of the .busy relay R240 in the trunk circuit 80, this circuit extending from the grounded line conductor C2I0 of the switching mechanism 300 in the selector repeater 55 is completely released and returned to its normal position, the set of switch springs S3l| is actuated into disengagement, thereby to interrupt the previously traced circuit for energizing the winding of the busy relay R240. The busy relay R240 then restores, thereby to interrupt, at the contacts 24|, the previously mentioned path for applying ground potential to the control conductor C203 of the trunk 8| in order to mark the trunk 8| as idle to the non-numerical automatic switches having access thereto.

At this point it is noted that the call initiated at the calling subscriber substation A in the distant exchange 10 and routed therefrom by way of the telephone line 1|, the non-numerical automatic switch 18, the trunk 8|, the trunk circuit 80, the trunk line 50, the selector repeater 55 and the trunk 35 to the first operator position 30 and answered at the first operator position 30 by operating the connect key K440 in the operator connecting apparatus 32, may be completed to another subscriber substation in the distant exchange 10 instead of to the subscriber substation D in the central exchange 20, in the manner previously explained. The operation of the apparatus in the central exchange 20 -to extend a call answered at the rst operator position 30 to a subscriber substation in the distant exchange 10 is described more fully hereinafter.

Also it is noted that the call on the telephone line 1| and routed by way of the previously traced piece of apparatus to the rst operator position 30 and answered thereat may have been initiated on the telephone line 1| due to the presence of a fault thereon. In other words, the call on the telephone line 1| answered at the rst operator position 30 may be a false call. After the operator at the first operator position 30 detects that the call routed thereto by way of the selector repeater 55 and the trunk 35 is a false call, she operates the key sender 33, thereby to cause a single predetermined digit to be registered in the first register 400 therein. After the single digit is registered in the rst register 400 in the key sender 33, operation of the selector repeater 55 is initiated, thereby to cause the wiper set of the switching mechanism 300 to be driven in the vertical direction a corresponding number of steps, in the manner previously explained. The wiper set of the switching mechanism 300 is then driven step by step in the rotary direction until it is driven eleven steps away from its normal position, this level in the associated contact bank terminating no trunks. When the wiper set of the switching mechanism 300 is thus operated in the vertical direction the set of `switch springs S3|4 is actuated into disengagement; and when the wiper set of the switching mechanism 300 is thus operated in the rotary direction the sets of switch springs S3|5 and S3|8 are actuated, the sets of switch springs S3| 0, S3|3 and S3||, S3|2 being respectively actuated into disengagement and engagement at this time, as previously explained. More particularly, the contacts 320 of the set of switch springs S3|8 are actuated into engagement, thereby to complete the previously traced alternative holding circuit for energizing the winding of the hold relay R360. When thus energized the hold relay R360 operates, thereby to condition the impulse relay R310 and the control relay R315 for operation in order to insure that the various registers in the key sender 33 are cleared. Also the contacts 3|1 of the set of switch springs S3|5 are actuated into dis-

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